Automatic pilot



June 10, 1958 P, A, NOXQN ET AL 2,838,258

AUTOMATIC PILOT Filed May 29, 1944 Sm JIA,

n@ mwN QQ NNN HUMSOW .U .i

l EN TORS PaulA.No:x:o1c

Plex! By Ala@ Mmccallw Abr/:zamlur A TrgR/VEY nited States Patent OAUTOMATIC PILOT Paul A. Noxon, Tenally, Alan M. MacCallum, Maywood,

and Norman B. Murphy, West Englewood, N. J., assignors to BendixAviation Corporation, Teterhoro, N. J., a corporation of DelawareApplication May 29, 1944, Serial No. 537,952

23 Claims. (Cl. 244-77) The present invention relates toan automaticnavigational control system adapted for use with dirigible craft and onewhich may be applied equally as well to the automatic control of eitherair or water borne craft.

Control systems of this general nature which have been heretoforeutilized have relied principally upon either pneumatic or hydraulicpressures, or a combination of both, for energizing the servo motors ofvarious control surfaces. As a result, known systems possessed certaindrawbacks, one being that where widely varying altitudes were traversed,the wide change in air densities affected the reliability of pneumaticsystems while extreme changes in temperatures produced undesirableeffects on hydraulic systems. Moreover, the numerous conduits requiredin such pressure systems were particularly vulnerable to gun lire wherethe systems were used on war craft.

An object of the present invention, therefore, is to provide a novel andimproved automatic navigational control system with the use of which theforegoing disadvantages are overcome.

Another object of the present invention is to provide a novel allelectric automatic pilot for aircraft of all sizes and uses wherebyoutstanding ease of controlv and complete maneuverability are obtained.The advantages of an `all electric automatic pilotk will be obvious. ForeX- ample, the operation of such a system will not be hindered by highaltitude flight or by flight through dust laden atmospheres. Moreover,the various electrical units constituting the pilot of the presentinvention are, to a certain extent, self-heating so that no difficultyis encountered in operation at low temperatures.

A further object of the invention is to provide a novel automatic pilotin which the displacement signals for each axis of control are derivedfrom a common electrical instrument and transmitted to operate electricservo motors of related control surfaces so that a rapid response on thepart of the control su-rfaces is obtained.

Another and further object is to provide a novel automatic pilot inwhich the various displacement signals may be readily addedalgebraically thereby making possible the free use of derivates andsuperimposed controls whenever and wherever required,

A still further object of the invention is to provide a novel allelectric, substantially contactless, A. C. steering system for dirigiblecraft. f

Another object is to provide an improved and novel all electricautomatic pilot providing control about three axes.

A further object is to provide a novel automatic threeaxes-of-controlpilot having a rate control superimposed on each axis. l

Another object is to provide an automatic pilot for dirigible craftwherein an electric servo motor is energized in response to a signalgenerated as a result of a craft departure from a prescribed position tooperate a control surface, a follow-back signal being generated as n aresult of the operation of rthe surface to modify operation of the motorin accordance therewith, and a rate signal being generated in proportionto the crafts angular velocity developed during craft departure from itsprescribed position to add to the displacement signal and oppose thefollow-back so that the control surface is applied more rapidly or, theoutward swing, a point being reached where the foiow-back signal isequal and opposite to the displacement and rate signals to stop themotor and con-trol surface, whereupon the craft returns to itsprescribed position. Gn return, the rate signal is reversed to opposethe displacement signal, but adds to the follow-back signal, whereby thecraft is prevented from overswinging its prescribed position once itattains that position, a reverse operation being applied to the controlsurface prior to the crafts return to its prescribed position to providea braking action thereon.

A further object is to provide a novel automatic pilot having adirection trim control which may be operated to develop any amount ofchange in heading desired with the automatic pilot engaged and withoutdisconnecting any of the component units from the system, the craftassuming straight flight once the new heading has been attained,

Another object is to provide a novel automatic pilot having an automaticturn control whereby any desired rate of turn may be set in, bank andpitch signals being automatically developed for the rate of turn calledfor.

The above and other objects land advantages of the resent invention willappear more fully hereinafter from a consideration of the detaileddescription which follows,V taken together with the accompanying drawingwherein one embodiment of the invention is illustrated. It is to beexpressly understood, how-ever, that the drawing is for the purpose ofillustration `and description only, and is not designed as a definitionof the limits of the invert tion.

The single figure of the drawing is a diagrammatic illustration of thenovel `automatic steering system of the present invention.

The novel automatic navigation control system comprising the subjectmatter of the present invention embodies a master instrument from whichdisplacement, bank and pitch signals are available for controlling thecraft in heading, as Well as in position about its transverse andlongitudinal axes. Repeater systems are interposed in the directiondisplacement channel whereby a change in heading of any desired amountmay be pre-set with the system engaged by injecting an artificialdisplacement signal into one of the repeaters, the craft changingheading until such time as the main displacement signai catches up withand corresponds to the pre-set signal whereupon straight flight isassumed by the craft on the new heading. Furthermore, an automatic turnprovision is made whereby any desired steady rate of turn may be imposedupon the craft, the proper direction displace ment, bank and pitchsignals for the predetermined rate of turn being automatically developedwithout imposing any positive load upon the master instrument normallycontrolling such functions. l

Referring now to the single figure of the drawing for a more detaileddescription of the present invention, a master instrument 10 is thereshown having a magnetic field pick-up device, in the form of a gyrostabilized earth inductor compass, the pick-up device comprising atriangular element 11, having laminated legs 12, 13 and 14, each havingwound thereon exciting windings 15, 16 and 17, each of the windingsbeing divided into two coils, each pair of coils surrounding a relatedlaminated leg and being connected in series opposed relation, thewindings being energized from a suitable source of alternating currentsuch, for example, as source 18. The secondary of device 11 comprises adelta connected coil 19 having three taps 20, 21 and 22 which connect byway U of suitable leads 23 with a three phase wound stator' 24 of aninductive coupling device mounted within a master indicator showngenerally by the reference character 26.

The theory and operation of the magnetic field pick-up device or earthinductor compass is described in greater detail in copending applicationSerial No. 445,102 filed May 29, 1942. For present purposes it is onlynecessary to point out that each leg 12, 13 and 14 is saturated andde-saturated twice for every cycle of the exciting current flowingwithin primary windings 15, 16 and 17 whereby the flux threading eachleg, due to the earths magnetic field, is expelled from and re-enterseach leg twice for each cycle of the exciting current. Since each pairof the coils of the primary windings 15, 16 and 17 of each leg are woundin series opposed relation no effect is induced on secondary coil 19 bythe exciting current itself. Except when the exciting current hasattained a substantially maximum value, either positive or negative, theearths magnetic eld is free to traverse each leg and as a resultvoltages are induced at the three taps 20. 21 and 22 of secondary coil19Kdiffering and dependent in value on the direction in which thepick-up element is positioned with reference to the earths magneticfield. The magnetic field pick-up device, therefore, operates as anearth inductor compass in that for every deviation from a prescribedcourse, however minute, the induced voltages at the three taps of thesecondary 19 will vary in accordance with deviation.

In order to provide a compass in which turning and acceleration errorsare, for all practical purposes, eliminated so that the tendency of thecompass to oscillate orV overswing is thereby prevented, element 11 issecurely fastened to a rotor casing 27 of a three-degree-of-freedomgyroscope having an electrically driven rotor, not shown, provided withvertical spin axis, mounted within casing 27 which supports the rotorfor oscillation about a first horizontal axis within a gimbal ring 28 byway of trunnions 29, the gimbal, in turn, being mounted for oscillationabout a second horizontal axis, perpendicular to trunnions 29,-Within arigid support carried by instrument 10, by means of outer trunnions 30.A suitable erection device may be provided for maintaining the rotorspin axis normally vertical as well as a caging apparatus for cagingand/ or uncaging the gyro whenever desired.

In addition to stabilizing the earth inductor compass, the gyroscope isalsoV provided with bank and pitch takeoffs in the form of inductivedevices 31 and 32, Vone of which comprises a three phase wound stator 33having inductively coupled therewith a wound rotor 34 which is movablewith trunnion 30, for example, and the other of which comprises a threephase wound stator 35 having inductively coupled therewith a wound rotor36 which is movable with trunnions 29. Both rotors 34 and 36 are tappedto a common conductor 37 for energization by source 18. In practice,take-ofr`s 31 and 32 are mounted directly on the gyroscope, take-off 31being on the bank axis and take-off 32 on the pitch axis, so that thethree principal control signals are derived from a single masterinstrument. The advantages arising from such an arrangement are obvious,for example, the weight of the whole system is reduced in that wherepreviously at least two gyroscopes were required, i. e., a directionaland artificial horizon gyroscope, the present system requires only onegyroscope. Moreover, the principal controls are concentrated in aVsingle casing whereby the device is simple to service and any diicultiesrapidly corrected. Y

For a condition of equilibrium, i. e., with the craft on a given headingand with all controls centralized, the

voltages within the three windings of stator 24 of coupling device 25Yof master indicator 26 will correspond to the voltage at the'three tapsof secondary coil 19 of the pick-up device and rotors 34 and 36 oftake-offs 31 and 3,2 will be at a given position with respect to theirrelated 2,838,258 f ,i f

. 4 stator windings 33 and 3S. At the same time, a rotor winding 38inductively coupled with stator 24 of coupling device 25 and carried bya shaft 39, suitably journalled within master indicator 26, Will bedisposed in an angular position with its electrical axis normal to theresultant magnetic field of the three windings of the stator so that thevoltages in the stator windings have no inductive effect on the rotorwinding. As soon, however, as the craft deviates from a prescribedheading, the voltages at the three taps of secondarycoil 19 will varycausinga variation in the voltages of each of the stator windings. Suchchange at the stator produces an angular change in the resultant of themagnetic field thereat and, since the electrical axis of the rotorwinding is no longer normal to the resultant of the field at the stator,a signal is induced within rotor winding 38 Which is proportional to theangle of craft deviation from its prescribed heading.

The electrical signal induced within rotor winding 38 is fed by means ofsuitable conductors 40 into a conventional vacuum tube'ampliier 41 andout therefrom by means of leads 42 to one phase winding 43 of a twophase induction rnotor 44, the second phase winding 45 of which iscontinuously energized from source 18 through a conventional frequencydoubler 46. Because, as has been shown, the frequency of the inducedcurrents within secondary 19 is twice the frequency of the excitingcurrent, doubler 46 is included to provide like frequencies in bothmotor windings and in addition, a suitable phase shifting network isembodied within the doubler so that the phases of theV current withinthe two motor windings will be substantially 90 apart.

Upon energization of motor phase winding 43, a rotor 47 is actuatedwhich carries a shaft 48 having a pinion 49 thereon meshing through areduction gear system 50 with a driven gear 51 secured to shaft 39 todrive rotor winding 38 to a null position, i. e., a position wherein theelectrical axis of the rotor winding'assumes a Vposition normal tothe'new resultant of the' stator eld at which point the signal in rotor38 approaches zero and phase winding 43 of motor 44 is de-energized andthe motor stops.

In order to provide an indication of the new heading or the amount ofdeviation off course, an indicating dial 52 is provided which is carriedby a shaft 53, journalled within the master indicator, the dial beingadapted for angular motion relative to a fixed index 54. Angular motionis imparted to the dial from rotor shaft 39 by way ofV a gear 55fastened to `the shaft and a gear 56 meshing therewith and having ahollow shaft V57 formed therewith and secured to dial shaft 53.Preferably shaft 57 is sleeved about shaft 53 and connected therewiththrough a Ycompensating mechanism as shown and described in copendingapplication Serial No. 516,488 filed December 3`1, 1943 and now PatentNo. 2,625,348. By observing dial 52, the pilot will immediately know hisheading and if desired the dial indication may be reproduced at severalremote stations and to this end shaft 53 carries a gear 58 for meshingwith a gear 59 drivably connected with the magnet rotor 60 of anelectromagnetic transmitter 61 whose stator winding connects with asimilar electromagnetic receiver at the remote station, such system forreproducing motion being essentially the same as that shown anddescribed in U. S. Patent No. 2,342,637 issued February 29, 1944.

ln driving rotor 38 of coupling device 25 to a new null in Vresponse `tocraft devi-ation from course, motor 44 also angularly displaces, from anormally null position, a wound rotor 62 relative 'to a three phasewound stator of an inductive transmitter device 63 with which the rotoris inductively coupled, the rotor'winding being connected by way of alead 64 with lead 37 for energization by source 18. By reason of thedisplacement of wound rotor 62 relative to its stator, voltages aredeveloped at the stator which Vmay be led directly to a rudder servosystem through an amplifier to actuate the rudder. Such an arrangement,however, has the one drawback that if it is desired to set in adisplacement signal independently of the earth inductor compass it couldnot be accomplished without disconnecting the compass from the system.

To the end that this may be accomplished without the necessity ofdisconnecting the compass from the system, novel provision is madewhereby the variation in voltages developed at the stator of transmitter63 is communicated by way of leads 65 to a three phase wound stator ofan inductive course setter device 66, normally located within a mastercontrol panel (not shown), the latter stator having inductively coupledtherewith a wound rotor 67. rIhe variation in voltages at the stator ofthe course setter develops an angularly movable ux vector relative torotor 67 whereby a signal is induced in the rotor proportional to theamount of craft deviation from a prescribed course.

Wound rotor 67 is mounted for angular motion relative to its woundstator by means of a conventionally journalled shaft 6S which carries aroller 69 thereon for engagement with a transversely movable disc 70supported for rotation by a shaft 7 which is fastened to a bracket 72,the free end of which is secured to a movably mounted bar '73. Inaddition to engaging roller 69, disc 70 also engages an integrating disc74 supported by a shaft 75 driven at a constant speed by a motor 76which is energized from source 18 by way of a lead 77 tapped toconductor 37, disc '70 normally engaging integrating disc 74 at thecenter thereof so that disc 70 is at rest and will not rotate at suchtime.

The signal induced in rotor 67 is communicated to the input of aconventional vacuum tube amplifier 78 by way of a lead 79 to a rstswitch A having contacts 1 and 2, contact 1 being closed at this point,lead 80 to a second switch B likewise having contacts 1 and 2, contact 1being closed at this point, a resistor 81 and a lead 82, the amplifieroutput being fed by way of a lead 83 to energize the variable phase 84of a two phase induction motor 85 having a rotor 86, the second phase 37being constantly energized from source 18 by way of a lead 88. Rotor 36is drivably coupled to move bar 73 through a gear 89 meshing with atoothed portion of the bar, the direction of movement of the bar beingdetermined by the phase of the signal fed to the variable phase of motor85.

Motion of bar 73 imparts a transverse movement to disc 70 from thecenter of rotating disc 74 whereupon disc 7i? rotates causing angularmotion of roller 69 and shaft 60 whereupon rotor 67 is moved toward itsnew A null position, i. e., toward a position wherein its electricalaxis will assume a position normal to the resultant ilux vector at thestator resulting from the displacement signal generated at compasselement 11. Bar 73 is also provided with a toothed portion 90 thereonfor engagement with a worm 91 carried by a shaft 92 which supports awound rotor 93 energized from source 18 by means of a lead 94, the rotorbeing inductively coupled with a three phase wound stator 95.

Wound rotor 93 is normally at an electrical null with respect to woundstator 95, however, as soon as motor 35 moves bar 73 to displace rotor67 toward its new null position, rotor L3 is displaced relative to itsstator 95 whereby a signal is induced therein, the latter signal beingopposite to the signal induced within rotor 67. Motion of rotor 67toward its new null position decreases the signal therein until a pointis reached where the signal of stator 95 is greater than the signal ofrotor 67 whereupon the stator signal predominates and motor 85 is drivenin a reverse direction moving rotor 93 back toward its original null androtor 67 away from the new null it was attempting to attain. At thispoint disc 70 is moved toward the center of integrating disc 74 so thatmotion of rotor 67 gradually decreases. As rotor 93 approaches its nullthe signal from rotor 67, though diminished, predominates and againreverses operation of motor 8S until rotor 67 is finally brought to itsnew null position and rotor 93 assumes its original null positionrelative to stator 95. Anti-hunting on the part of the system is thusovercome and an indicating device 96 may be associated with roller 69whose indication will correspond with the indication of masterinstrument 26 when rotor 67 has been brought into its new null position.When the indications of master instrument 26 and instrument 96correspond, the system is in condition to be engaged by the human pilotto automatically control craft direction of ilight.

To obtain automatic control of a rubber surface 97, contacts 1 ofswitches A and B are opened and their contacts 2 are closed. Thereafter,any craft deviation from prescribed course manifests itself in a signalgenerated by compass element 11, reproduced at the inductive transmitterdevice 63 and the stator of course transmitter device 66, acorresponding signal being induced within rotor 67 thereof which is fedby lead 79 through contact 2 of switch A to the input of a conventionalvacuum tube amplifier 97a the output of which is fed by a lead 98 to thevariable phase 99 of a rudder servo induction motor 100, the secondphase 101 of which is constantly energized from source 18 by means ofleads 102 and 103. 1nterposed between motor and a rudder actuating shaft104 is a normally disengaged clutch 105 provided with an actuatingsolenoid 106 which is connected through a normally open servo switch 107by a lead 108 with a suitable source of direct current (not shown).

For automatic control, switch 107 is closed by the human pilot wherebysolenoid 106 is energized to engage clutch and thereby establish adriving connection between motor 100 and rudder 97. An electricalfollowup is provided between rudder 97 and compass 11 in the form of aninductive follow-back device having a threephase wound stator 109inductively coupled with a wound rotor 110 energized from source 18 byway of leads 37, 77, 88 and leads 111 and 112, the rotor being mountedfor angular motion by shaft 104. Actuation of shaft 104 by motor 100produces angular displacement of wound rotor 110 from a normally nullposition relative to stator 109 whereby a follow-back signal is inducedin the stator and fed by way of a lead 113 into amplifier 97a to bethere superimposed upon the displacement signal developed at rotor 67 inthe manner more fully shown in our copending application Serial No.516,488 iiled December 3l, 1943. The follow-back signal generated instator 109 is in opposition to the direction displacement signal andincreases with rudder displacement as a result of the continuedoperation of motor 100 until a given point is reached, at which time thesignal within stator 109 is exactly equal and opposite to the directionsignal to thereby wash-out the direction signal at which time motor 100is de-energized and rudder 97 has reached an outward position inproportion to the direction signal. The sensitivity of the ruddercontrol may be controlled in the manner disclosed in Fig. 4 of ourabove-mentioned copending application Serial No. 516,488 by means of avariable resistor 109e connected across two of the windings of thestator 109, the resistance being varied by a slide contact 10912.

With rudder 97 in its applied position and motor 100 cle-energized, thecraft will begin to return to its predetermined and prescribed course.in doing so, the direction signal generated by the pick-up device 11starts to diminish in value while the follow-hack signal of stator 109,being at a maximum,becomes predominating and energizes motor 100 in areverse direction to start bringing the rudder back to a neutralposition. With reverse operation of motor 100, the signal in stator 109diminishes as rotor 110 thereof is brought back to its normally nullposition wherein, unless another direction signal is being generated bythe pick-up device, the rudder and the direction signal generating meansare in syn` YT7 chronism. This condition of synchronism is desirably`obtained without the provision of mechanical follow-up connections inthe nature of cables, for example, between the rudder and the pick-updevice. v

The control of the rudder by the direction displacement signal alonewillinvariably result in oscillations in that the craft, as it is broughtback on course, tends to overswing, only to be brought back on courseonce more and then overswing in the original direction of departure. Thenet result is to cause the craft to weave about its course rather thanto remain steadily thereon.

By impressing upon the direction signal, another signal that isdependent upon the crafts angular velocity or rate of turn, it is atonce possible to control craft oscillation whereby dead beat steeringand extreme stability under all weather conditions can be obtained. Tothis end, a rate of turn gyro is provided which comprises anelectrically driven rotor 114 connected by way of lead S8 with source 1Sthrough lead 77, the r'otor having normally horizontal spin axis andmounted by way of trunnions 115 within a gimbal ring 116 which, in turn,is mounted by way of outer trunnions 117 and 118 for oscillation about asecond horizontal axis perpendicular to the spin axis. Suitableresilient members such as springs 119, for example, are connected totrunnion 117 to yieldably restrain gyro precession to a rate of turnfunction as is known in the art.

To generate a signal proportional to the rate of craft turn, asdetermined by the rate gyro, an inductive trans- Ymitting device isprovided comprising a three phase wound stator and a wound rotor 121inductively associated therewith, the rotor being connected to lead 37for energization by source 18. Rotor 121, moreover, is mounted ontrunnion 118 for angular motion therewith.

The stator of inductive device 120 has a voltage generated in each ofits three windings proportional, respectively, to the angular positionof each of the windings relative to rotor 121 and is connected by a lead122 to the input of amplifier 97a. With rotor 121 in a given nullposition relative to its stator, i. e., a position in which the crafthas no angular velocity, no signal will be fed to the amplifier throughlead 122. As soon, however, as a departure from course occurs and thecraft also develops an angular velocity, rotor 121 is moved angularlyrelative to its stator producing induced voltages within the statorwindings, the signal developed as aV result of such a change beingimpressed upon the directionand follow-back signals within amplifier97a.

Thus three signals, i.V e., direction, rate and follow-back are mixed oradded algebraically within the amplifier to control operation ofinduction motor 1%. With such provision and during an initial craftdisplacement from a prescribed course, the rate signal aids thedirection signal and opposes the follow-back signal so that rudder isapplied more rapidly than it would be by the direction tr signal aloneand duringV a return to course the rate signa (the crafts angularvelocity now being inlan opposite direction) opposes the directionsignal but adds with the follow-back signal so that the craft isprevented from overswinging from its prescribed course onceit returnsthereto. This is in the nature'of an anticipatory control which acts togive the rudder a slight deection in an opposite directionwhen itapproaches on course so that it is braked to remain on such course.Y ltis thus apparent that the static rudder position by the foregoingprovision ismade to be algebraically proportional to the sum of the rateand direction signais.

Signals for controlling the craft about its bank and pitch axes arederived from take-offs 31 and 32 located on gyro trunnions 29 and 30within master instrument 10. The stator 33 of take-off 31 is connectedby leads 125 to a three phase Wound stator 126 of an inductive banktrim'V device having a wound rotor 127 inductively coupled therewith,the rotor being connected to the input of an amplifier 128 by way of alead 129. Rotor 8 127 issupported upon a shaft 130 connected to a lever131, ythe'free end of which is-connected to a roller 133 whichcooperates with a cam 134 fastened to bar 73 so that motion of the barin one direction rotates the roller to angularly displace shaft androtor 127 in one direction and motion of the bar in an oppositedirection rotates the roller to langularly displace shaft 130 andVrotor' 127'in an opposite direction;

Stator 3S of the pitch take-off device 32, on .the other hand, connectsby way of leads 135 with a three phase wound stator 136, of a pitch trimdevice, having a wound rotor 137 inductively coupled therewith, therotor being connected to the input of an amplifier 138 by way of a lead139. Rotor 137 is supported upon a shaft 1411 connected to one end of acrank 141 whose free'end is secured to a roller 142 adapted forengagingY two oppositely inclined cams 143 and 144 so that Vmotion ofthe bar in one direction rotates roller 142 `along surface `144 tooscillate the crank about shaft 111i) as a pivot and, therefore, rotor137 in one direction while motionV of the bar in an opposite directionrotates roller cam surface 143 to oscillate the crank as well as rotor137 in the same direction, the arrangement being such that motion of bar73 'in either direction produces angular displacement of rotor 137 inone direction oniy.

Three phase wound stators 126 and 136 of the bank and Vpitch trimdevices are `actually repeaters for any bank and pitch signals generatedat take-offs 31 and 32 at the gyro. A displacement of the craft in pitchand bank produces relative motion of wound rotors 3ft and 35 withrespect to their related stators 33 and 35 whereby unbalanced voltagesaredeveloped at the stator windings which are communicated to statorwindings 126 and Due to such unbalance in stator windings 126 and 136.the electrical axis of rotors 127 and 137 will longer normal to theresultant of the two elds at the stators so that signals will be inducedin each of the rotors proportional to the bank and pitch of the craft.The two signals are amplified within amplifiers 123 and 133 and theoutputs thereof are fed by leads 145 and Vto the variable phases 147 and148, respectively, of aileron and elevator servo induction motors 149and 1.5i?, the second phase 151 of motor 149 being constantly energizedfrom source 18 through leads 162, 1113 and a lead 152, and the secondphase 153 of motor 151i being constantly energized from source 13through leads 1112, 163 and a lead 154. Y

interposed between motors V149 and 159 and their respective aileronandelevator actuating shafts 155 and 155 are normally disengagedclutches 157 and 153, oi

which is provided with actuating solenoids 159, 1d?, the solenoids beingconnected through normally oper. switches 161 and 162 by way of leads163 and 164 with a suitable source of direct current (not shown).

Before switches 161 and 162 are closed to cause engagement of clutches157 and 158 to establish a drivable connection between motors 149 and15@ and their respective control surfaces 165 and 166, it should bedetermined as to whether or not a condition of synchro-msm existsbetween the control system and the control surfaces. For example, theailerons maybe in a normally alized position but Ia bank signal mayexist within rotor 127 and at the output of amplifier 123 or there mayhe no signal'at the rotor but'the ailerons may be displaced.

' In either case motors 149 and 151i would he running as d pitch or tothe switch 151, for

a result of the signals due to bank an L displaced surfaces so thatclosing Vor example, would develop severe jolts on the system and thecraft.

Connected across the outputs of amplifiers 123 andV theindicators willshow the existence o f the bank andV ce no pitch conditions. In order toeliminate the Vbank and pitch signals, stators 126 and 136 of the bankand pitch trim devices are mounted for angular motion relative to woundrotors 127 and 137 by way of bank and pitch trim knobs 169 and 174).These knobs may be turned to angularly displace their respective stators126 and 136 until the resultants of the magnetic fields therein assumenormal positions relative to the electricai axis of rotors 127 and 137at which time no signals are induced in either of the rotors andindicators 167 and 162 indicate a no bank and no pitch condition.

1f, o-n the other hand, no bank or pitch signals exist in rotors 127 and137 but ailerons 165 and elevators 166 are displaced from a centralizedposition such condition will be registered upon indicators 167 and 168,the reason being that inductive follow-back devices are providedcomprising three phase wound stators 1"?1 and 172, each of which isinductively associated with a related wound rotor 173 and 174, therotors being 'tapped to lead 111 by way of leads 175 and 176 forenergization from source 18. Rotor 173 is mounted for angular movementwith shaft 155 relative to stator 171 and is at an electrical null withrespect to its stators when ailerons 165 are in a centralized position.ailerons are deliected from a central position, rotor 173 is displacedto a position other than a null position at which time a signal isinduced in stator windings 171 and fed therefrom by a lead 177 toamplifier 128 where indicator 167 registers such unbalance. 'Thesensitivity of the aileron control may also be varied in the manner.disclosed in our aforesaid copending application Serial No. 516,488 bymeans of a variable resistor 171e connected across two of the windingsof stator 171, the resistance being varied by means of a slide Contact171b- Rotor 174 of the elevator follow-back device, on the other hand,is mounted for angular movement with shaft 156 and is at an electricalnull with respect to its stator when elevator 166 is in a centralizedposition. if the elevators are deected from a central position, rotor174 is displaced to a position other than a null position at which timea signal is induced in the stator windings 172 and fed therefrom by alead 178 to amplifier 138 where indicator 168 registers such unbalance.`The sensitivity of the elevator control may likewise be varied in themanner disclosed in our aforesaid copending application Serial No.516,488 by means of a variable resistor 172e connected across two of thewindings of stator 172, the resistance being varied by means of; a slidecontact 172b.

The human pilot may then operate the aileron and elevator controlsurfaces manually until they are centralized whereupon rotors 173 and174 return to their null position so thatthe signals at stators 171 and172 drop to zero and indicators 167 and 168 show this condition. Thesystem is now in synchronism with the control surfaces and switches 161and 162v may be operated to connect servo motors 149 and 150.with theirrespective control surfaces 165 and 166. Thereafter, any craftdisplacement in bank or pitch will result in signals induced in bank andpitch take-oils 31 and 32 which are also induced within rotors 127 and137 and amplified within ampliiiers 128 and 138 to energize variablephase 14=7 and M8 of motors 149 and 150. The

motors, being thus energized, drive ailerons 165 and ,ele-

vators 166 from their central position and simultaneously therewithrotors 173 and 174 of the follow-back devices are displaced from theirelectrical nulls relative to stators 171 and vlill induced in stators171 and 172 are exactly equal and opposite to the bank and pitch signalsat which time motors 149 and 159 are energized and the ailerons andelevators have reached an outward position proportional to 'the bank andpitch signals.

With ailerons and elevators 166 in their applied positions and motors149 and 150 de-energized, the craft will begin to return to acentralized position. in doing so the bank and pitch signals attake-Otis 31 and 32 diminish in value while the follow-back signals ofstators 171 and 172, being at maximum, become predominating and energizemotors 149 and 150 in a reverse direction to start bringing the aileronsand elevators back to their neutral positions wherein the controlsurfaces and the bank and pitch generating means are synchronized. As inthe case of the direction control channel, the condition of synchronismis obtained without the use of mechanical follow-up connections such ascables between the ailerons and elevators and the bank and pitchcontrols.

By impressing upon the bank and pitch signals, another signal which isdependent upon the crafts angular velocity or rate of turn developedduring the bank and pitch or climb of the craft, it is possible tocontrol oscillation about the bank and pitch axis which might otherwiseoccur. To this end, therefore, rate of turn gyros are provided, eachcomprising electrically driven rotors 179 and 180 connected by Way ofleads 181 and 182 with source 18 through lead 37, rotor 179 having anormally vertical spin axis and rotor 180 having a normally horizontalspin axis displaced 90 from the position of the spin axis of rotor 114of the rate gyro in the direction channel, rotor 179 being mounted byway of trunnions 183 within gimbal ring 184 which, in turn, is mountedby way of outer trunnions 13S, 186, for oscillation about a horizontalaxis parallel with the crafts longitudinal axis and rotor 18) beingmounted by way of trunnions 187 within a gimbal ring 188 which ismounted by way of outer trunnions 189, 196, for osciilation about avertical axis perpendicular to the crafts longitudinal axis. Springs 191and 192 are connected to trunnions and 189, respectively, to yieldablyrestrain gyro precession to a rate of turn function.

In order to generate signals proportional to the rate of the craftsangular velocity developed during craft bank and pitch, inductivetransmitting devices are provided comprising three phase wound stators193 and 194 having inductively associated therewith wound rotors 195 and196, the rotors being connected for energize.- tion from source by wayof leads 197 and 198 tapped to lead 37. Rotors 195 and 196, moreover,are carried for angular motion relative to their stators by trunnions186 and 190 and when the craft is centralized about its bank and pitchaxes the' two rotors are at an electrical null with respect to theirstators. As soon as craft bank and pitch occurs an angular velocity isdeveloped about the crafts transverse axis as well as about itslongitudinal axis causing rotors 179 and 1S!) to precess and therebydisplace the rotors relative to their statcrs 193 and v194 inducing inthe latter signals which are led to the amplifiers 123 and 138 by wayof: leads 199 and to be there superimposed upon the bank and pitchsicnals and the related follow-back signals in the same manner and forthe same purpose as described in connection with the directiondisplacement signal.

Novelprovision is made, furthermore, for changing the direction ofiiight of the craft from one prescribed course to a second andpredetermined course with the automatic pilot engaged and withoutdisconnecting the compass element 11 from the system. T o this end, thestator of the course'setter device 66 is mounted for angular movementrelative to its wound rotor 6'7 and to the end that such statordisplacement may be accomplished,a direction trim knob 201 is provided.

Actuation of ltnob`291 produces angular motion of the course setterstator so that a signal is inducedV within Y rotor 67 thereof. Thesignal is fed from rotor 67 by way of lead 79 to the input of amplifier97a whereupon variable phase 99 of motor 100 is energized to applyrudder whereby the Vcraft turns toward its new course an angular amountcorresponding to the amount of change of course set in by knob 201.During the turn a follow-back signal and a rate signal are developed tomodify the operation of motor 100 and rudder 97 in the mannerhereinabove described. The craft course in a flat turn until such timeas the signal developed from the earths magnetic field by element 11 andreproduced in the stator windings of the inductive transmitter device 63is suiiicient to move the resultant of the magnetic field at the statorof the course setter device 66 to a position normal to the electricalaxis of rotor 67 whereupon the induced signal in the rotor diminishes toZero and the craft will have reached its new course. Thereafter, theautomatic pilot maintains the craft on its new course until and unlessknob 201 is again operated.

A further novel and desirable feature of the automatic pilot of thepresent invention is that an automatic turn may be imparted to the craftwithout disconnecting compass'element 11 from the system. To this end,the three phase wound stator 95 of the inductive follow-up device ismounted for angular displacement relative to its rotor 93, an automaticturn control knob 202 being provided to accomplish this purpose. Bysetting knob 202, a steady rate of turn of the craft Vmay be developedwith the correct bank and pitch signals automatically set in for thegiven rate of craft turn.

In manually displacing automatic turn knob 202,- stator 95 is angularlydisplaced from its normally null position relative to its4 rotor 93whereupon a signal is induced in the stator and fed by way of a lead 82to amplifier 78Y and out therefrom to energize variable phase S4 ofmotor 85 whereupon the motor moves bar 73 in one direction or another,depending upon the direction of the turn set in by knob 202, to displacedisc 70 relative to integrating disc 74 whereby wound rotor 67 of thecourse setter device 66 is angularly displaced from its null positionrelativev to its stator, a signal being induced within rotor 67 and fedtherefrom through amplifier 97a to operate rudder surface 97 and therebyimpart a constant rate of turn to the craft.

Simultaneously with the displacement of rotor 67 relative to its statorby bar 73, the bar, in moving likewise displaces rotors 127 and 137 ofthe bank and pitch trim devices relative to theirvrespective stators 126and 136 whereby the correct bank and pitch signals are developed toAoperate the aileron and elevator surfaces the correct amount for theparticular rate of turn of the craft set in by knob 202, it being notedthat whether the turn be to the left or right of a given course upelevator is 1 provided in either case.

Follow-up motor 85, in response to the signal developed at stator 95 bythe turn knob, will continue to move bar 73 until the latter has movedrotor 93 into a new null position relative to stator 95 whereupon thesignal in the latter drops to zero and motor S5 becomes changes l ArJcraft manually, contacts 2 of switches A and B are opened and contacts 1thereof closed while servo switches 107, 161 and 162 are openedwhereupon clutches 105, 157 and 158 disconnect the rudder, aileron andelevator surfaces from their respective servo motors 100, 149 and 150.For automatic flight, on the other hand, the human pilot opens contacts1 of switches A and B and closes contacts 2 thereof as well as servoswitch 107 of the rudder channel. cate condition of synchronism,switches 61 and 162 of the aileron and elevator channels are closed andthereafter, whenever the craft deviates from a prescribed course and/ora predetermined attitude the system is immediately effective to returnthe craft to its prescribed course and/or attitude.

Separate amplifiers 97, 128 and 138 have been shown for the direction,bank and pitch channels, however, one amplifier embodying all threechannels may be used equally as well, such amplifier being shown anddescribed in our above-mentioned copending application Serial No.516,488. Moreover, the various inductive devices have been shown ashaving wound stators and wound rotors inductively coupled therewith,however, electromagnetic devices comprising wound stators having unwoundmagnetic rotors inductively coupled therewith of ,the characterdescribed and claimed in the above referred to U. S.

de-energized- At this point disc 70 has been displaced ment from thesystem, the turn being completed wheneverk knob 202 is returned manuallyto a normal position.

To disengage the automatic steering system of the pres- 75 Patent No.3,342,637 may be used in place thereof.

There has thus been provided a novel all electric automatic pilotwherein the principal control signals, i. e., direction, bank and pitchare derived from a single master instrument. Moreover, novel provisionis made for a direction trim adjustment whereby the craft, with theautomatic pilot engaged, may be forced to change course without thenecessity of disconnecting the compass element 11 from the system.Furthermore, an automatic turn may be impressed upon the craft wherebyupon the operation of a single knob a steady rate of turn signal isdeveloped together with the proper bank and pitch signals required forthe particular rate of turnv called for. Y

Although but a single embodiment of the invention has been illustratedand described in detailfor controlling a mobile craft about all three ofits axes, it is to be expressly understood that the invention is notlimited thereto. Various changes may also be made in the design andarrangement of the parts without departing from the spirit and scope ofthe invention as the same Will now be understood by those skilled in theart. For example, some of the statorsof the inductive devices may be twophase wound instead of three, or three phase wound stators may beprovided but only two of the phases would be sufficient to perform thevarious functions described. For a definition of the limits of thepresent invention reference will be had primarily to the appendedclaims.

We claim:

1. In an automatic pilot for an aircraft having rudder, aileron, andelevator control surfaces thereon for maintaining the craft on apredetermined course and in a predetermined attitude, servo motors foreach of said control surfaces, reference means on said craft forgenerating a signal in response to a departure of said craft from saidpredetermined course, means comprising bank and pitch devices foroperating said aileron and elevator servo motors in response to adeparture of said kcraft from said predetermined attitude, meanscomprising a signal repeater interposed between said reference means andsaid rudder servo motor for normally actuating said rudderrrnotor inaccordance with the signal generated by said reference means, and meanscomprising a single automatic turn control for simultaneously actuatingsaid signal repeater and said bank and pitch devices whereby a steadyrate of turn with the proper bank and pitchY therefor is limposed onsaidcraft.

When indicators 167 and 16S indi-V assaess 2. ln an automatic pilot foran aircraft having rudder, aileron and elevator surfaces thereon formaintaining the craft on a predetermined course and in a predeterminedattitude, a servo motor for each of said control surfaces, referencemeans on said craft for generating a signal in response to a departureof said craft from said predetermined course, means comprising bank andpitch devices for operating said aileron and elevator servo motors inresponse to a departure of said craft from said predetermined attitude,means comprising a signal repeater device interposed between saidreference means and said rudder servo motor for normally actuating saidrudder motor in accordance with the signal generated by said referencemeans, and means comprising a single automatic turn control forsimultaneously actuating said signal repeater device and said bank andpitch devices whereby a steady rate of turn with the correct angle ofbank and pitch is imposed on said craft.

3. in an automatic pilot for an aircraft having rudder, aileron andelevator surfaces thereon for maintaining the craft on a predeterminedcourse and in a predetermined attitude, a servo motor for each of saidcontrol surfaces, reference means on said craft for generating a signalin response to a departure of said craft from said predetermined course,means comprising bank and pitch devices for operating said aileron andelevator servo motors in response to a departure of said craft from saidpredetermined attitude, means comprising a signal repeater deviceinterposed between said reference means and said rudder servo motor fornormally actuating said rudder motor in accordance with the signalgenerated by said reference means, a driving member for actuating saidsignal repeater device to develop a steady displacement signal foroperating said rudder motor and for simultaneously actuating said bankand pitch devi es whereby signals are developed thereby for actuatingsaid aileron and elevator motors, and automatic turn control means forenergizing said driving member.

4. In an automatic pilot for an aircraft having rudder, aileron andelevator surfaces thereon for maintaining the craft on a predeterminedcourseV and in a predetermined attitude, a servo motor for each of saidcontrol surfaces, reference means on said craft for generating a signalin response to a departure of said craft from said predetermined course,means comprising bank and pitch devices for operating said aileron andelevator servo motors in response to a departure of said craft from saidpredetermined attitude, means comprising a signal repeater deviceinterposed between said reference means and said rudder servo motor fornormally actuating said rudder motor in accordance with the signalgenerated by said reference means, an integratingk device for actuatingsaid signal repeater device whereby a steady displacement signal isdeveloped for operating said rudder motor, means comprising a drivingmotor for operating said integrating device and for actuating said bankand pitch devices whereby signals are developed for actuating saidaileron and elevator motors, and automatic turn control means forenergizing said driving motor.

5. An automatic control device for a mobile craft having a controlsurface movable for maintaining the craft on a predetermined course,comprising a servo motor for operating said surface, reference means onsaid craft for generating a signal in response to a departure of saidcraft from said course, means comprising a signai repeater deviceinterposed between said reference means and said servo motor fornormally actuating said servo motor in accordance with the signalgenerated by said reference means, an integrating device for actuatingsaid signal repeater device to develop a steady displacement signal indpendently of said reference means for actuating said motor, a drivingmotor for operating said integrating device, and a displaceableautomatic turn controller for energizing said driving motor to an iff:

14 extent corresponding to the displacement of said controlier.

6. ln an automatic pilot for a craft having rudder, aileron and elevatorcontrol surfaces for maintaining the craft on a predetermined course andin a predetermined attitude, a motor for each of said control surfaces,means comprising a master instrument for developing direction, bank andpitch signals in response to a departure of said craft from saidpredetermined course and attitude for operating the moto-rs of saidcontrol surfaces, means comprising a signal repeater' device interposedbetween said instrument and said rudder motor for normally actuatingsaid rudder motor in accordance with said direction signal, bank andpitch trim devices interposed between said banl'. and pitch signals andsaid aileron and elet ,tor motors, and means comprising a singleautomatic turn control for simultaneously actuating said signal repeaterdevice and said bank and pitch trim devices whereby a steady rate ofturn with the correct angle of bank and pitch for that turn is imposedon said craft.

7. in an automatic pilot for a craft having rudder, aileron and elevatorcontrol surfaces for maintaining the craft on a predetermined course andin a predetermined attitude, a motor for each of said control surfaces,a master instrument for developing direction, bank and pitch signals inresponse to a departure of said craft from said predetermined course andattitude for operating the motors of said control surfaces, meanscomprising a signal repeater device interposed between said masterinstrument and said rudder motor for normally actuating said ruddermotor in with said direction signal, bank and pitch trim devicesinterposed between said master instrument and said aileron and elevatormotors, an integrating device for actuating said signal repeater devicewhereby a steady displacement signal is developed for operating saidrudder motor, means comprising a driving -motor for operating saidintegrating device and for actuating said bank and pitch devices wherebysignals are developed for actuating said aileron and elevator motors,and automatic turn control means for energizing said driving motor.

8. An automatic steering system for a craft having a rudder, comprisingan inductive device having a multipolar stator winding and a rotorwinding in inductive relation with said stator winding, a two-phasealternating current motor connected to actuate the rotor winding of saidinductive device, a source of alternating current, means connecting saidsource to energize one phase of said motor, direction responsive meanscomprising an induction device including m ti-polar Winding connected tothe multi-polar winding of said inductive device and a single phasewinding energized by said source of alternating current whereby anotheralternating current is generated in the multi-polar winding of saidinduction device, means connecting the rotor winding of said inductivedevice energi the phase of said motor whereby the latter rotates toactuate the rotor winding of said inductive device upon relative angulardisplacement of said direction responsive means in azimuth, anelectrical transmitting device connected to said motor for transmittingan electrical signal proportional to the relative angular displacementof said direction responsive means, a two-phase alternating currentservo motor for actuating the rudder of said craft, means connecting onephase of said servo motor for energization by said source of alternatingcurrent, means comprising a course setter device connecting said signaltransmitting device to energize the other phase of said servo motorwhereby the latter actuates said rudder in accordance with the relativeangular displacement of said direction responsive means in azimuth, anintegrating device for actuating said course setter device to develop asteady displacemnet signal to energize said other phase of said servomotor independently of said direction respon e means and withoutdisconnecting said signal transmitting means from said course assenso(i5 setter device, a driving member for operating said integratingmeans, and means comprising an automatic turn control for energizingsaid driving member.

9. An automatic turn provision for a craft having rudder and a servomotor for operating said rudder comprising a signal generator forenergizing said servo motor, an integating mechanism for operating saidgenerator, a control motor for va .L d in c ic' mechanism, a two partsignal means for developing command signal upon relative displacement ofsaidV parts from a null position, a turn knob for displacing one of saidparts to provide a command signal for energizing said control motor as afunction of a pre-selected amount of turn, and means operable by saidcontrol motor for displacing said other part to reestablish a nullposition.

10. An automatic control provision for a craft having a ruddercomprising a servo motor for operating said rudder, first and secondsignal generators, said rst signal generator energizing said servomotor, an integrating mechanism for operating said first generator, acontrol motor for variably operating said integrating mechanism, saidsecond signal generator energizing said control motor, and a turn knobfor actuating said second generator.

having rudder, 1 i -fgether with servo motors for op urfaces, anautomatic turn mechanism for said pilot comprising a turn signalgenerator for energizing said rudder servo motor, bank and pitch trimdevices for energizing said aileron and elevator servo motors, anintegrating mechanism for operating said signal generator, a controlmotor for variably operating said mechanism and said bank and pitch trimdevices, and a control for said motor.

l2. in an automatic control devi., for ha movable control surfacethereon adapted for manual `operation, a servo motor normallydisconnected from said surface but adapted for connection thereto forthe automatic operation thereof, reference means on said craft forgenerating a signal in response to a departure of said craft from apredetermined course for energizing said motor, means for drivablyconnecting said motor to said surface, and an inductive devicepermanently connected for movement by Vsaid surface for producing asecond signal in response to the operation of said surface for mixingwith said first signal to modify the operation cf said motor, and meansfor maintaining the sum of said signals at zero when said servornotor isdisconnected from said surface whereby the servomotor may be connectedto said surface without transient effects..

13. ln an automatic control device for a craft having movable controlsurface thereon adapted for manual operation, a servo motor normallydisconnected from said surface but adapted for connection thereto forthe operation thereof, reference means on said craft for generating asignal in response to a departure of said craft from a predeterminedcourse for energizing said motor, clutch means drivably connecting saidmotor to said surface, and means comprising a variable inductive devicehaving Van angularly displaceable wound member drivably comiectcd foractuation by said surface for produca.:T a second g in response to theoperation of said surface for mixing with said rst signal to modify theoperation of said motor, and means for maintaining the sum of saidsignals at zero during the time said servomotor is disconnected fromsaid surface.

V14, Control apparatus for an aircraft comprising: motor means forcontrolling said craft; a balanceable control means including aplurality of controllers; attitude means responsive to movement of saidcraft for adjusting one controller; means driven by said motor means andconnected to a second controller; a third controller; Vpower means foroperating said 'third controller; means for alternatively connectingsaid motor means or said power means to said control means for operationthereby whereby said power means may adjust its controller at one rateon unbalance of said balanceable control means; and further means foroperating said power means to position said third controller at adifferent rate while said motor means is controlled by said controlmeans.

l5. Control apparatus for an aircraft having a control surface forcontrolling the aircraft about its axis, said apparatus comprising:control surface power means, control means for said power means,operating means for said control means including a plurality of signalgenerators and means for combining generated signals; means responsiveto change of heading of said aircraft for actuating a signal generatorin proportion to the magnitude of said change; means for actuating asecond signal generator from said heading change responsive means inproportion to the magnitude and duration of deviation, said secondsignal generator remaining actuated upon removal of said change inheading; and means for actuating a third signal generator from saidpower means.

16. Control apparatus for an aircraft comprising motor means forcontrolling said craft; a balanceable control means including aplurality of controllers; attitude means responsive to movement of saidcraft for adjusting one controller; means driven by said motor means foradjusting a second controller; power means for adjusting a thirdcontroller; means for alternatively connecting said motor means or saidVpower means to said control means for operation thereby, whereby saidpower means may adjust said third controller on unbalance of saidbalanceable control means while said motor means is not controlled bysaid control means; and further means for operating said power means topositionV said third controller while said motor means is controlled bysaid control means.

17. Control apparatus for an aircraft comprising motor means forcontrolling the craft, control means having a plurality of controllers,reference means responsive to the deviation of said craft from apredetermined heading for adjusting one controller, follow-up meansdriven by said motor means for adjusting a second controller, powermeans for adjusting said third controller, means for alternativelyoperating said motor means or said power means from said control meanswhereby said power means may adjust said third controller upon unbalanceof said control means to rebalance said control means while said motormeans is not controlled from said control means and a-turn knob foroperating said power means to position said third controller asafunction of a preselected turn while said motor means is controlled fromsaid control means.

18. Control apparatus for an aircraft having a control surface forcontrolling the attitude of an aircraft about its axis, comprising powermeans adapted to be associated with and disassociated from said controlsurface, control means for said power means including a plurality ofsignal generators and means for combining generated signals, meansresponsive to a change of attitude of said craft for actuating a signalgenerator in proportion to the magnitude of said change, synchronizingmeans for actuating a second signal generator from said changeresponsive means in proportion to the magnitude and duration of saidchange when said power means is disassociated from said surface, saidsecond signal generator remaining actuated when said power means isassociated with said surface, and means for actuating a third signalgenerator from said power means.

19. Control apparatus for an aircraft having a control surface forcontrolling the attitude of an aircraft about its axis, comprising powermeans adapted to be associated with and disassociated from said controlsurface, control means for said power means including a plurality ofsignal generators and means for combining generated signals, meansresponsive to a change of attitude of said craft for actuating a signalgenerator in proportion to the magnitude of said change,synchronizassaas ing means for actuating a second signal generator fromsaid change responsive means in proportion to the magnitude and durationof said change when said power means is disassociated from said surface,said second signal generator remaining actuated when said power means isassociated with said surface, means for actuating a third signalgenerator from said power means, and further means for actuating saidsynchronizing means when said power means is associated with saidsurface to cause said craft to assume a new attitude.

20. A system for controlling the surface of a craft, comprisingelectrical signal means having two parts for developing a signalcorresponding in sense and magnitude to the direction and extent ofrelative displacement of said parts from a null position, craftreference means for positioning one of said parts, driving means forpositioning the other of said parts, power means adapted to beassociated and disassociated with said control surface and selectivemeans for maintaining said two parts at Zero signal condition byoperating said driving means to position said second part at a nullposition relative to said rst part when said power means is notassociated with said surface and for operating said power means toposition said surface so that said craft reference means positions saidsecond part to a null position when said power means is associated withsaid surface.

21. A control system for operating tbe surface of an aircraft to controlthe course of the craft, comprising power means for operating saidsurface, reference means for generating an error signal in response to adeparture of said craft from a predetermined course, repeater meansinterposed between said reference means and said power means forreceiving said signal and developing a control signal proportionalthereto, said repeater means being connectable with said power means forenergizing said power means by said control signal to operate saidsurface, integrating means for actuating said repeater means, automaticturn means for operating said integrating means, and means forselectively operating said integrating means from said automatic turnmeans or from said control signal, whereby said automatic turn means mayoperate said integrating means to impose a steady rate of turn on saidcraft when said repeater means is connected for energizing said powermeans and said control signal operates said integrator to synchronizesaid repeater means with said reference means when said repeater meansis not connected to energize said power means.

22. A system for controlling the surface of a craft to maintain thecraft on a predetermined course, compris- "i ing power means for movingsaid surface, reference means for generating a signal in response todeparture of said craft from said course, means interposed between saidreference means and said power means for normally actuating said powermeans in accordance with said signal but operable for assuming primarycontrol of said power means to impose turn on said craft, an integratorfor operating said last named means, a control member for developing aturn signal, and means responsive to said turn signal for operating saidintegrator so as to reduce said turn signal to zero.

23. A structure for use with a balanceable control apparatus of the typein which a main controller and a follow-up controlled device, whichcontrols a condition sensed by the main controller conjointly controlsan operable controlling mechanism to maintain it in a null or unoperatedcondition to cause the controlling mechanism to position the controlleddevice in accordance with changes in the condition of said maincontroller and terminate operation of said controlling mechanism, saidmechanism comprising an amplifier and a balanceaole electrical controlsignal providing network connected to the amplier wherein the maincontroller and the follow-up controlled device are relatively remotelypositioned in said network, said mechanism also comprising, adjustablemeans in said controlling mechanism network remote from said maincontroller and operable to also place said controlling mechanism in anull condition, automatic means adapted to respond to said controllingmechanism for positioning said adjustable means, and selective switchingmeans connected to said controlling mechanism for selectively connectingeither said automatic means or said controlled device to saidcontrolling mechanism.

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